1. Field of the Invention
The present invention relates to a method of determining a heating amount that is adequate in fusion splicing optical fibers, a method of fusion splicing that utilizes such determination method, and a fusion splicer for use in such fusion splicing method.
2. Description of the Background Art
In fusion splicing of optical fibers, determination of the heating amount with which end portions to be spliced are heat-melted is vitally important in achieving a low loss connecting. The heating amount that is adequate in fusion splicing of optical fibers varies depending on the type of optical fibers (for example, optical fibers having fluorine in its cladding tend to melt easier), or the environmental factors (temperature, humidity, air pressure, windiness, and so on). Furthermore, while arc discharge is often used in heating optical fibers, it has been known that the number of times the arc discharge electrodes have been used also affects the heating temperature.
Thus, a test arc discharge is normally conducted at the time of fusion splicing in order to adjust and configure the heating amount. A fusion splicer is generally equipped with an image-capturing device and image processing means in order to allow visual observation of the end portions of the optical fibers to be spliced, and it has been known to adjust and configure the heating amount using the image processing means.
Japanese Patent Application Publication No. 5-150132 discloses a method of configuring the heating amount based on the retraction of the end surfaces of the optical fibers caused by the arc discharge heating. In this method, a gap L1 between the end surfaces of the optical fibers before the arc discharge heating and a gap L2 between the end surfaces of the optical fibers after the arc discharge heating are measured (FIGS. 4A and 4B), whether the difference between the gap L1 and the gap L2 (melt back) is within an appropriate range is determined, and the heating amount (arc discharge power) is increased or decreased if the melt back is outside the appropriate range.
Japanese Patent No. 2685152 discloses a method of controlling the arc discharge current based on the area of a glowing portion (light emitting portion) that is generated in the fusion-spliced portions of the optical fibers 19 during the arc discharge heating. In this method, the brightness of the light emitting portion is segmented with the image processing to obtain an area of the light emitting portion and estimate the heating intensity. The result is fed back to the control unit and the arc discharge current is controlled so that the heating temperature is within a predetermined range.
In fusion splicing of optical fibers, an arc discharge test is conducted whenever the type of optical fiber changes, whenever the environmental factors change, and when a long period passes. Thus, reconfiguration of adequate heating amount is conducted relative frequently. Consequently, an arc discharge test is desired to be conducted easily, precisely, and as few times as possible. However, it is practically very difficult to conduct a precise arc discharge test at a construction side such as inside a manhole.
In the method disclosed in the Japanese Patent Application Publication No. 5-150132, at every measurement of the melt back, the arc discharge heating has to be conducted after the fibers have cut, which requires a lot of work. Furthermore, since the melt back is measured after the arc discharge heating is conducted, the heating amount cannot be adjusted or configured on a real time basis. Accordingly, it takes a substantial amount of labor and time to conduct the measurement.
In the case where the heating amount is measured while measuring the area of the light emitting portion that emits light during the arc discharge heating, as in the method disclosed in Japanese Patent No. 2685152, the ends to be spliced tend to become too thin when the heating is excessive. On the other hand, the core misalignment tends to result due to an impact of the fibers being pushed toward one another when the heating is insufficient. In such cases, it is difficult to remedy the problems even by changing the heating amount. Accordingly, the fusion splicing has to be conducted all over again. When the method is performed as an arc discharge test, as in the case of Japanese Patent Application Publication No. 5-150132, the fibers have to be cut and the arc discharge heating has to be performed anew at every measurement. Accordingly, it takes a substantial amount of labor and time to conduct the measurement.